OLED (Organic Light-Emitting Diode) displays are one of current hot spots in the research area of the flat panel display. Compared with liquid crystal (LC) displays, the OLED displays have advantages such as low power consumption, low production cost, self-illumination, wide angle of view, fast response, and so on. Currently, the OLED displays have begun to replace traditional LC displays (LCDs) in the display areas such as cell phones, personal digital assistants (PDAs), digital cameras, etc. The design of pixel driving circuits is a core technology of the OLED displays, and thus has significant research value.
Different from the thin film transistor (TFT)-LCDs (TFT-LCDs) which use a stable voltage to control the brightness, the OLED displays are current-driven, which need a stable current to control the light emitting.
Normally, one pixel circuit is usually corresponding to one sub-pixel, and each pixel circuit comprises at least one data line, one voltage line providing an operating voltage, and a plurality of scan signal lines. As a result, the corresponding fabrication process would be complicated, and the pixel pitch is hard to be reduced.